knee powered portable charger

1. International Journal on Emerging Technologies (Special Issue on ICRIET-2016) 7(2): 341-346(2016)
ISSN No. (Print) : 0975-8364
ISSN No. (Online) : 2249-3255
Power Generating Knee straps with Hints at End
Amar Vatambe
Department of Mechanical Engineering,
BKIT, Bhalki, Karnataka, INDIA
(Corresponding author: Amar Vatambe)
(Received 28 September, 2016 Accepted 29 October, 2016)
(Published by Research Trend, Website: www.researchtrend.net)
ABSTRACT: Human power is an attractive energy source. Muscle converts food into positive mechanical
work with peak efficiencies of approximately 25%, comparable to that of internal combustion engines. while
a typical mobile phone consumes a modest 0.9 W electrical requiring a 18 g Li-ion battery for 3 hours of talk
time, a typical laptop computer requires a 720 g Li-ion battery to satisfy its 28 W electrical power needs,
lasting less than 4 hours. The power generation which is designed to fit onto the outside of the knee, is
circular and consists of two spur gears. The spur gear rotates as the knee joint goes through a walking
motion. The knee itself is an ideal starting point for energy generation as it has a large change in angle during
walking and does so at significant speeds. A spur gear attached to the joint could therefore generate large
amounts of power.
Key words: Pyro electric, DC motor, Battery, Heel strike etc.
I. INTRODUCTION
From mobile phones to laptop computers, society has
become increasingly dependent on portable electronic
devices. Because batteries almost exclusively power
these devices, and the energy per unit mass in batteries
is limited, there is a trade-off between device power
consumption, battery weight and duration of operation.
This trade-off is particularly severe in the design of
powered prosthetic joints that need to be lightweight
while performing their sophisticated task over a full day
of typical use. The manufacturers of the C-leg, Rheo
Knee and Proprio Foot indicate that their devices
operate for more than 36 hours from a single charge of
a battery that weighs about 230 g battery equating to an
average power consumption of less than 1W electrical.
Substantial improvement to the operating time or
performance of a portable device, while avoiding the
unattractive solution of simply heavier batteries,
requires an alternative to current battery technology.
A. Pyro electric
The pyro electric effect converts a temperature change
into electric current or voltage. It is analogous to the
piezoelectric effect, which is another type of
ferroelectric behaviour. Pyro electricity requires time-
varying inputs and suffers from small power outputs in
energy harvesting applications due to its low operating
frequencies. However, one key advantage of pyro
electrics over thermoelectric is that many pyro electric
materials are stable up to 1200 ⁰C or higher, enabling
energy harvesting from high temperature sources and
thus increasing thermodynamic efficiency.
B. Heel strike
Several devices have been built to generate energy from
heel-strike motion. Some devices use the energy from
the relative motion between the foot and the ground
during the stance phase (the phase in which the foot is
on the ground). Others use the energy from the bending
of the shoe sole. In both cases, the device aims to use
the energy that would otherwise have been lost to the
surroundings. An example of such a device is a
hydraulic reservoir with an integrated electrical
magnetic generator that uses the difference in pressure
distribution on the shoe sole to generate a flow during
the gait cycle.
II. LITERATURE SURVEY
A. Literature Survey
A team of scientists from the U.K.’s Cranfield
University invented pizzicato knee-joint energy
harvester. The result is a wearable piezoelectric device
that converts knee movement into electricity but it is
not produce higher energy densities. The research
community, within both academia and industry, has
been addressing these problems. They are invented new
gadget called biomechanical energy harvester. It is
consist of the some gear attached through micro-
generator. The gear and micro-generators is that use to
produce electricity.
et

2. Vatambe 342
Part of the mass and the mechanical complexity was
due to the implementation of gears which increase the
rotational speed of the electromagnetic generator to
increase its efficiency.
B. Vibrational Energy Harvesting Using Mems
Piezoelectric generators (2009)
In recent years, energy harvesting using piezoelectric
materials has become a very popular research topic.
Various device sizes and structures have been tested,
but it is difficult to compare power measurements as
device fabrication and experimental methods vary from
paper to paper. In an effort to standardize comparisons
in spite of these changing parameters, the dependence
of generator power output on device dimensions has
been investigated. Though MEMS scale devices have
been produced, comparatively little work has been done
using aluminum nitride (AlN). This project utilizes AlN
due to its ease in processing and potential for on-chip
integration. By operating at a MEMS scale, the benefit
is that arrays of piezo generatorscan be placed on the
same die. With the process advantages of AlN, a long
term goal of an integrated power-harvesting chip
becomes feasible. However, theoretical results of
scaling predict that raw power output and even power
per unit volume will decrease with scaling.
C. RF-based Wireless Charging and Energy Harvesting
Enables New Applications and Improves Product
Design (2012)
RF energy is currently broadcasted from billions of
radio transmitters around the world, including mobile
telephones, handheld radios, mobile base stations, and
television/ radio broadcast stations. The ability to
harvest RF energy, from ambient or dedicated sources,
enables wireless charging of low-power devices and has
resulting benefits to product design, usability, and
reliability. Battery-based systems can be trickled
charged to eliminate battery replacement or extend the
operating life of systems using disposable batteries.
Battery-free devices can be designed to operate upon
demand or when sufficient charge is accumulated. In
both cases, these devices can be free of connectors,
cables, and battery access panels, and have freedom of
placement and mobility during charging and usage.
D. Kinetic energy-harvesting shoes a step towards
charging mobile devices (2011)
Although you may not be using a Get Smart-style shoe
phone anytime soon, it is possible that your mobile
phone may end up receiving its power from your shoes.
University of Wisconsin-Madison engineering
researchers Tom Krupenkin and J. Ashley Taylor have
developed an in-shoe system that harvests the energy
generated by walking. Currently, this energy is lost as
heat. With their technology, however, they claim that
up to 20 watts of electricity could be generated, and
stored in an incorporated rechargeable battery.
III. HARDWARE DESCRIPTION
In this chapter the block diagram of the project and
design aspect of independent modules are considered.
Block diagram is shown in fig.1:
Fig. 1. Block Diagram.
A. Spur gear Mechanism
Gears are machine elements used to transmit rotary
motion between two shafts, normally with a constant
ratio. The pinion is the smallest gear and the larger gear
is called the gear wheel.. A rack is a rectangular prism
with gear teeth machined along one side- it is in effect a
gear wheel with an infinite pitch circle diameter. In
practice the action of gears in transmitting motion is a
cam action each pair of mating teeth acting as cams.
Gear design has evolved to such a level that throughout
the motion of each contacting pair of teeth the velocity
ratio of the gears is maintained fixed and the velocity
ratio is still fixed as each subsequent pair of teeth come
into contact.
Fig. 2. Gear.
B. D.C Generators
Generator principle: An electrical generator is a
machine which converts mechanical energy (or power)
into electrical energy (or power).
Fig. 3. Dc Generator.

3. Vatambe 343
Induced e.m.f is produced in it according to Faraday's
law of electromagnetic induction. This e.m.f causes a
current to flow if the conductor circuit is closed.
C. Working of Geared DC Motor
Geared DC motors can be defined as an extension of
DC motor which already had its Insight details
demystified here. A geared DC Motor has a gear
assembly attached to the motor. The speed of motor is
counted in terms of rotations of the shaft per minute
and is termed as RPM .The gear assembly helps in
increasing the torque and reducing the speed. Using the
correct combination of gears in a gear motor, its speed
can be reduced to any desirable figure. This concept
where gears reduce the speed of the vehicle but
increase its torque is known as gear reduction. This
Insight will explore all the minor and major details that
make the gear head and hence the working of geared
DC motor.
External Structure. At the first sight, the external
structure of a DC geared motor looks as a straight
expansion over the simple DC ones.
Fig. 4. Gear Dc Motor.
The lateral view of the motor shows the outer protrudes
of the gear head. A nut is placed near the shaft which
helps in mounting the motor to the other parts of the
assembly.
Engine-generator. An engine-generator is the
combination of an electrical generator and an engine
(prime mover) mounted together to form a single piece
of self-contained equipment. The engines used are
usually piston engines, but gas turbines can also be
used. And there are even hybrid diesel-gas units, called
dual-fuel units. Many different versions of engine-
generators are available - ranging from very small
portable petrol powered sets to large turbine
installations. The primary advantage of engine-
generators is the ability to independently supply
electricity, allowing the units to serve as backup power
solutions.
Human powered electrical generators. A generator
can also be driven by human muscle power (for
instance, in field radio station equipment).
Human powered direct current generators are
commercially available, and have been the project of
some DIY enthusiasts. Typically operated by means of
pedal power, a converted bicycle trainer, or a foot
pump, such generators can be practically used to charge
batteries, and in some cases are designed with an
integral inverter. The average adult could generate
about 125-200 watts on a pedal powered generator, but
at a power of 200 W, a typical healthy human will reach
complete exhaustion and fail to produce any more
power after approximately 1.3 hours portable radio
receivers with a crank are made to reduce battery
purchase requirements, see clockwork radio.
E. Charging Circuit
Fig. 5. Charging Circuit.
From the above circuit diagram, we can see that the 18v
AC is being converted to 18V pulsating DC which is in
turn converted to smooth DC with the help of the
Capacitor. This 18V Smooth DC is converted to 12V
DC by the Voltage Regulator 7812. At the output of the
regulator, we get some spikes which are not desirable.
These spikes are removed with the help of another
capacitor used. We can get 12V Steady DC at the
output terminal which can be indicated if the LED
glows.
F. Rechargeable battery
A rechargeable battery, storage battery, or accumulator
is a type of electrical battery. It comprises one or more
electrochemical cells, and is a type of energy
accumulator. It is known as a secondary cell because its
electrochemical reactions are electrically reversible.
Rechargeable batteries come in many different shapes
and sizes, ranging from button cells to megawatt
systems connected to stabilize an electrical distribution
network. Several different combinations of chemicals
are commonly used, including: lead–acid, nickel
cadmium (NiCd), nickel metal hydride (NiMH), lithium
ion (Li-ion), and lithium ion polymer (Li-ion polymer).
Fig. 6. Battery.

4. Vatambe 344
Charge Mode. Constant voltage charge (constant
voltage and constant resistance charge) is
recommended.
Charging current is limited, so be sure to charge via a
charge-limiting resistor.
The specified charge voltage must also be observed.
If you are considering adopting constant current and
constant voltage charge mode, contact SII.
Charge Voltage Range. Observe the specified
charging voltage range.
* Charging at a voltage higher than the upper limit may
degrade the electrical characteristics
or lead to leakage or bursting.
* Charging at a voltage lower than the lower limit
significantly reduces discharge capacity.
Charging rechargeable batteries. Type into the
calculator your rechargeable battery’s capacity number,
normally can be red on the battery body e.g. 1700 mAh
( milli-ampere-hours ). Then select the battery type/size
in the left column ( NiMH – NiCd – AAA – AA – C –
D – 9V ( 9 volt )) and in the right side select a current
output ( electric power output ) of your charger in mA.
Fig. 7. Charging Circuit kit.
IV. METHODOLOGY
A. Walking mechanics and energetics
On average, there is no net mechanical work performed
on the body during walking at a constant speed on level
ground as there is no net change in kinetic or potential
energy. This is accomplished by a number of sources–
including muscle, tendon, clothing and air resistance–
contributing to perform equal amounts of positive and
negative mechanical work. Selectively engaging a
generator at the right times and in the right locations
could assist with performing negative mechanical work
on the body, replacing that normally provided by other
sources such as muscle. This is similar to how
regenerative braking generates power while
decelerating a hybrid car. We have termed this form of
energy harvesting generative braking as the electricity
is not reused to directly power walking but is available
for other uses.
In principle, generative braking can produce electricity
while reducing the metabolic cost of walking. When
performing positive mechanical work, active muscle
fibres shorten while developing force, converting
chemical energy (i.e. metabolic energy) into mechanical
energy. The peak efficiency of positive muscle work is
approximately 25%. That is, a muscle producing 1 W
mechanical requires 4W metabolic and dissipates 3W as
heat. When performing negative work, muscle fibres
develop force but are compelled to lengthen by an
external force. This braking system is not passive–
muscles require metabolic energy to perform negative
work. The peak efficiency of negative work production
is approximately -120%. That is, a muscle producing -1
W mechanical requires 0.83 W metabolic and dissipates
1.83 W heat. We refer to generating electricity by
increasing positive muscle work–as is the case with
hand cranks and bicycle generators–as conventional
generation. Generating electricity in this manner will
cause a relatively large increase in effort, while
electricity generation that results in a decrease in
negative muscle work will result in a relatively small
decrease in effort.
While muscles are the only source of positive work in
walking, there are other sources of negative work in
addition to muscle. These include air resistance,
damping within the shoe sole and movement of soft
tissue. These are considered passive sources of negative
work in that, unlike muscle, they don't require
metabolic energy to dissipate mechanical energy. While
the contribution of air resistance and shoe sole damping
are thought to be small during walking, the quantitative
contribution of soft tissue movement to negative work
is not yet clear. While muscles do not perform all of the
required negative mechanical work during walking, it is
believed that they perform a substantial fraction.
Nevertheless, it is possible for negative work by an
energy harvesting device to replace negative work by a
passive source, such as soft tissue, resulting in no
change in metabolic cost to the user.
Fig. 8. Knee Strap Structure.
Typical knee joint mechanics and muscle activity
during walking (subject mass = 58 kg; speed = 1.3 m/s;
step frequency = 1.8 Hz. Data from). A) Knee joint
angle where 180 degrees is full knee extension. B) Knee
joint angular velocity using the convention that positive
angular velocity is motion in the extension direction. C)
Knee joint torque with the convention that extensor
muscle torques are positive. D) Knee joint power. E)
Rectified and filtered electromyograms (EMG) from
one knee flexor muscle (solid line) and one knee
extensor muscle (dashed line).

5. Vatambe 345
V. DESCRIPTION
A. Device Design
The biomechanics of walking presented four main
challenges for designing a device to harvest energy
from the motion of the knee joint. The first challenge
was to determine an effective mechanism for converting
biomechanical power into electrical power. This
generator had to be worn on the body so it needed to be
small and lightweight. The second challenge was to
design a mechanism for converting the intermittent, bi-
directional and time-varying knee joint power into a
form suitable for efficient electrical power generation.
The third challenge was to optimize the system
parameters in order to maximize the electrical power
generation without adversely affecting the walking
motion. At any given point in the walking cycle, there is
only a certain amount of knee mechanical power
available–attempting to harvest too much power will
cause the user to limp or stop walking while harvesting
too little results in less electrical power generated. The
final design challenge was to determine a mechanism
for selectively engaging power generation during swing
extension to achieve generative braking.
Fig. 9. Basic Mechanism structure.
The simulated device reaction torque, efficiency and
generated electrical power depend on the transmission
gear ratio and the external electrical load. A) A contour
plot of simulated device reaction torque at different
combinations of gear ratio and external load.
B. Device Description
We operated the device in four different modes. In the
generative braking mode, the control system selectively
engaged and disengaged power generation to target the
swing extension negative work region. In the
continuous generation mode, the control system was
deactivated, the power generation circuit was always
completed, and electrical power was generated
whenever the generator was in motion. In the flexion
dissipation mode, the control system engaged power
generation during the swing and stance knee flexion
phases to completely dissipate the kinetic energy in the
transmission and generator that had accumulated during
knee extension. This testing mode was used to
determine the amount of torque and mechanical power
produced due to friction and inertia during the knee
extension phases, independent of generator back-EMF.
In the disengaged mode, the roller clutch was manually
disengaged so that the transmission was never in
motion. This testing mode served as a control condition
for human subject experiments to account for any
physiological changes that resulted from carrying the
added mass independent of physiological changes
resulting from energy harvesting.
VI. RESULTS
The project “Power-Generating Knee Strap Hints At
End For Batteries” was designed such that to generate
electrical power as non-conventional method by simply
walking with knee strap set up using spur gear
mechanism. Non-conventional energy using walking or
running using converting mechanical energy into the
electrical energy.
Using these device, the cost of harvesting by
conventional generation would be approximately 6.2–
each additional Watt of electricity would require 6.2
Watts of metabolic power. This was estimated from the
peak device efficiency (64.7%) and the peak efficiency
of performing positive muscle work (25%). The COH
in generative braking (0.7 ± 4.4)–calculated from
dividing the additional metabolic power required for
generative braking relative to that required for the
disengaged mode (5 ± 21 W) by the measured electrical
power (4.8 ± 0.8 W)–was substantially lower than for
conventional generation indicating that it did not
depend entirely upon additional positive muscle work to
produce electricity. That we measured a slight increase
in metabolic cost indicated that generative braking did
not simply replace negative muscle work. If it had done
so, we would have expected a 7.3 W decrease in
metabolic cost calculated by dividing the measured
electrical power by the product of the device efficiency
(54.6%) and the efficiency of performing negative
muscle work (-120%). The likely source for the
additional metabolic cost is the positive muscle work
required to overcome the added resistance during stance
extension (Figure 6). The continuous generation COH
(2.3 ± 3.0) fell between that for generative braking and
that for conventional generation indicating that its
electrical power production (7.0 ± 0.7 W) was partially
by conventional generation with a high COH and
partially by generative braking with a very low COH.
VII. CONCLUSION
We have developed a biomechanical energy harvester
for generating electricity from walking. The device
operated about the knee to take advantage of the large
amount of negative work that muscles perform about
this joint. It used a one-way clutch to transmit only knee
extensor motions, a spur gear transmission to amplify
the angular speed, a brushless DC rotary magnetic
generator to convert the mechanical power into
electrical power, and a control system to determine
when to engage and disengage the power generation
based on measurements of knee angle.

6. Vatambe 346
A customized orthopaedic knee brace supported the
hardware and distributed the device reaction torque
over a large leg surface area. For convenient
experimentation, the control system resided on a
desktop computer and resistors dissipated the
generated electrical power. The device was efficient
and the control system was effective at selectively
engaging power generation. Consequently, subjects
were able to generate substantial amounts of electrical
power with little additional effort over that required to
support the device mass. While we have focused on
harvesting energy from swing extension, power
generation is possible from other periods of the gait
cycle. At the beginning of the stance phase, for
example, the knee flexes while the knee extensor
muscles generate an extensor torque performing
substantial negative work to aid in the redirection of
the centre of mass velocity (Figure 1). The amount of
available energy at moderate walking speeds is only
slightly less than that at the end of swing and it
increases strongly with speed. Consequently, our
initial device design attempted to also harvest energy
from stance flexion. It used two oppositely-oriented
roller clutches on the input shaft, causing the
generator to spin in the same direction regardless of
the direction of knee motion, and an extra stage of
gearing to increase the gear ratio during flexion.
While the higher gear ratio was required to better
match the low angular velocity and high torque
characteristics of stance flexion mechanical power
(Fig. 1), the transmission and generator friction and
inertia presented awkwardly large resistive forces
during the high angular velocity swing flexion phase.
This was not an issue for knee extension where power
generation was engaged during swing extension,
when knee angular velocity is high, and disengaged
during stance extension, when knee angular velocity
is low. While this drawback forced us to disregard
power generation during stance flexion, power
generation could be doubled with a more suitable
design. For now, generative braking during stance
flexion is best considered a hypothesis that must be
tested empirically as it is not yet known how much of
the negative work during this period is stored and
subsequently returned during stance extension.
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